Ovarian Function and Estrogen-Progesterone Physiology

The ovary produces both the female germ cells and the steroid hormones that govern the reproductive cycle. Across each cycle a cohort of follicles develops, one usually becomes dominant and ovulates, and the residual structure forms a corpus luteum; estrogen dominates the growth phase and progesterone the post-ovulatory phase.

Definition

Ovarian function is the combined gametogenic and endocrine activity of the ovary: follicular synthesis of estrogens through the cooperation of theca and granulosa cells, and luteal production of progesterone, regulated by LH and FSH and feeding back on the hypothalamic-pituitary axis.

Scope

This topic covers how ovarian follicles synthesise estrogens, how the corpus luteum produces progesterone, and how these hormones change across the cycle. It explains the cooperation between theca and granulosa cells in steroidogenesis. It is a reference account of normal physiology rather than clinical guidance.

Key concepts

• Ovarian follicle and follicular development
• Theca and granulosa cells
• Aromatisation of androgens to estrogens
• Estradiol as the principal follicular estrogen
• Corpus luteum and progesterone
• Inhibin from granulosa cells
• Cyclic feedback on the pituitary

Key theories

Two-cell, two-gonadotrophin model

Estrogen synthesis in the developing follicle requires cooperation between two cell types under two gonadotropins: LH stimulates theca cells to make androgen precursors, which FSH-stimulated granulosa cells then aromatise to estrogen.

Mechanisms

Follicular estrogen synthesis follows the two-cell, two-gonadotrophin model: luteinizing hormone stimulates theca cells to produce androgens from cholesterol, and these androgens diffuse to the neighbouring granulosa cells, where follicle-stimulating hormone has induced the aromatase enzyme that converts them into estrogens, chiefly estradiol. The steroidogenic enzymology that supports these conversions is part of the broader pathway of steroid hormone synthesis. After ovulation the ruptured follicle is remodelled into the corpus luteum, which secretes large amounts of progesterone along with estrogen. Granulosa-cell inhibin contributes negative feedback on pituitary FSH, and the rising and falling steroid levels relay feedback to the hypothalamic-pituitary axis that organises the cycle.

Clinical relevance

These mechanisms explain how the ovary generates the hormonal signals that pattern the reproductive cycle and prepare reproductive tissues. The theca-granulosa partnership accounts for why both gonadotropins are needed for normal estrogen production. This entry describes physiology and the basis of evidence and is not a basis for diagnostic or treatment decisions.

History

Classic endocrine and biochemical studies established that ovarian estrogen production is a shared task between theca and granulosa cells driven by two gonadotropins, a synthesis captured in the two-cell, two-gonadotrophin model and refined as the steroidogenic enzymes were characterised. Parallel work clarified the luteal production of progesterone and the role of inhibin, completing the picture of the ovary as a cyclic endocrine organ.

Key figures

• Stephen Hillier
• Walter Miller
• Jan-Ake Gustafsson

Seminal works

• hillier-1994
• miller-1988
• nilsson-2001

Frequently asked questions

How does the ovary make estrogen?

Through the two-cell, two-gonadotrophin model: LH-stimulated theca cells produce androgens, which FSH-stimulated granulosa cells aromatise into estrogens such as estradiol.

Where does progesterone come from in the cycle?

Mainly from the corpus luteum, the structure formed from the follicle after ovulation, which secretes progesterone during the second half of the cycle.